Traveling wave electrode photoelectric detector and method for improving bandwidth thereof

Abstract

The invention provides a traveling wave electrode photoelectric detector and a method for improving the bandwidth thereof. The method comprises the steps that an optical signal enters a waveguide through grating coupling; light in the waveguide is divided into multiple beams of optical signals with equal optical power by adopting a multi-stage power beam splitter, and the multiple beams of optical signals with equal optical power are preset with non-uniformly designed optical path differences; inputting a plurality of beams of optical signals with equal optical power into a plurality of corresponding photoelectric detectors; when each photoelectric detector generates a light current, the light current is propagated in the traveling wave electrode and is reflected, and a plurality of light currents have phase differences; and the reflected light current and the light current transmitted to the output end are overlapped and output together. According to the method, the bandwidth of the traveling wave electrode photoelectric detector can be effectively improved, and expected requirements are met.

Description

Technical Field

[0001] The present invention relates to the field of photodetectors, and particularly to a traveling-wave electrode photodetector and a method for improving its bandwidth. Background Art

[0002] With the continuous increase in the integration degree of electronic chips, electrical interconnection faces a series of problems such as large signal delay, small transmission bandwidth, high power consumption, serious heating, and strong signal crosstalk. Therefore, optical interconnection emerges as the times require. High-frequency photonic links have advantages such as high bandwidth, low power consumption, and strong electromagnetic interference resistance. High-speed and high-saturation power photodetectors are important optoelectronic devices in RF (radio frequency) photonic links.

[0003] However, there is a trade-off between high bandwidth and high-saturation output power in current waveguide photodetectors. In order to achieve high bandwidth, waveguide photodetectors need to ensure that the absorption region is very small to reduce the junction capacitance and transit time. However, in the case of high optical power input, the small absorption region will limit the output saturation current due to the space charge effect and thermal effect. Therefore, it is difficult for waveguide detectors to be compatible with both high bandwidth and high saturation characteristics at the same time. The traveling-wave electrode photodetector solves this contradiction. First, the high input optical power is divided into multiple small-power beams and respectively input to multiple photodetectors, and then the output currents of all photodetectors are aggregated. The increase in the number of photodetectors solves the problem that the small absorption region limits the saturation output power.

[0004] However, in order to maintain high bandwidth when the number of photodetectors increases, traditional traveling-wave electrode photodetectors need to meet two limiting conditions, namely velocity matching and impedance matching. Velocity matching enables the output photocurrent reaching each photodetector to be synchronized with the output photocurrent of the photodetector here; impedance matching designs a terminal resistor that can absorb the reflected photocurrent, reducing the influence of the reflected photocurrent caused by impedance mismatch and the photocurrent propagating in the opposite direction to the input end on the bandwidth. These two conditions limit the spacing between each photodetector and the optical path difference of the optical paths input to each detector, and also make it difficult for the bandwidth of the traveling-wave electrode photodetector to exceed that of a single photodetector. Summary of the Invention

[0005] (I) Technical Problems to be Solved

[0006] Aiming at the above deficiencies, the main object of the present invention is to provide a method for improving the bandwidth of a traveling-wave electrode photodetector. This method makes the bandwidth of the traveling-wave electrode photodetector reach the optimum by designing the optical path difference, and regulates the impedance distribution by designing the size of the terminal resistor and the spacing between each detector, so that the photocurrent reflected due to impedance mismatch and the photocurrent propagating towards the output end will not cause the bandwidth of the traveling-wave electrode photodetector to decrease due to the phase difference.

[0007] (2) Technical solution

[0008] In order to achieve the above object, in the first aspect of the present invention, a method for improving the bandwidth of a traveling-wave electrode photodetector is provided, which is characterized by comprising: a light signal enters a waveguide through a grating coupler; a multi-stage power splitter is used to split the light in the waveguide into multiple optical signals with equal optical power, wherein the multiple optical signals with equal optical power are preset with a non-uniformly designed optical path difference; the multiple optical signals with equal optical power are input into corresponding multiple photodetectors; when a photocurrent is generated in each photodetector, the photocurrent propagates in the traveling-wave electrode and generates reflection, wherein there is a phase difference between the multiple photocurrents; the reflected photocurrent and the photocurrent propagating towards the output end are superposed with each other and output together.

[0009] In the above solution, the method further comprises: a termination resistor is arranged at the end side of the traveling-wave electrode, and the termination resistor absorbs and reflects the photocurrent generated by the photodetector, wherein the size of the termination resistor is 20 - 80 Ω.

[0010] In the above solution, the corresponding relationship between the optical path difference and the phase difference of the photocurrent is:

[0011]

[0012] wherein, f is the frequency of the radio frequency signal generated by the photodetector, n is the effective refractive index of light transmitted in a single-mode silicon waveguide, c is the speed of light in vacuum, Δl is the optical path difference, and is the phase difference of the photocurrent.

[0013] In the above solution, each photodetector adopts double-end incidence.

[0014] In the above solution, in the direction from the input end to the output end of the traveling-wave electrode, the distance between every two photodetectors increases in sequence, and the distance is 0 - 500 μm.

[0015] In the above solution, each stage of the power splitter is a 1×2 multimode interference type optical power splitter.

[0016] In the above solution, the waveguide is a single-mode silicon waveguide with a thickness of 220 nm.

[0017] In the second aspect of the present invention, a traveling-wave electrode photodetector is provided, comprising: a grating, a waveguide, a power splitter, a photodetector, a traveling-wave electrode, a termination resistor and an output end, wherein; the grating, the power splitter and the photodetector are sequentially connected through the waveguide, the photodetector is connected to the traveling-wave electrode, and both ends of the traveling-wave electrode are respectively connected to the termination resistor and the output end.

[0018] In the above solution, the optical signal enters the waveguide through grating coupling; the power splitter divides the optical signal in the waveguide into multiple optical signals with equal optical power, and the multiple optical signals are incident from both ends of multiple photodetectors; each photodetector generates a photocurrent, and the photocurrent propagates in the traveling-wave electrode and generates reflection, and the reflected photocurrent is superposed with the photocurrent propagating towards the output end and jointly output to the output end.

[0019] (III) Advantageous Effects

[0020] The technical solution of the embodiment of the present invention has at least the following advantageous effects:

[0021] (1) The present invention increases the regulation of the photocurrent phase by the non-uniform optical path design and the optimization design of the impedance distribution, greatly improving the degree of freedom of design and having a larger optimization space, and having a wide application prospect in the field of traveling-wave electrode photodetectors.

[0022] (2) The method for improving the bandwidth of the traveling-wave electrode photodetector proposed by the present invention can be compatible with the CMOS process, with low manufacturing difficulty and low cost, which is conducive to large-scale integration.

[0023] (3) The present invention enables the bandwidth of the traveling-wave electrode photodetector to be effectively improved to meet the expected requirements. Description of the Drawings

[0024] Figure 1 Schematically shows a flowchart of a method for improving the bandwidth of a traveling-wave electrode photodetector according to an embodiment of the present invention;

[0025] Figure 2 Schematically shows an overall framework diagram of an 8-stage PD traveling-wave electrode detector array according to an embodiment of the present invention;

[0026] Figure 3 Schematically shows an overall framework diagram of a 4-stage PD traveling-wave electrode detector array according to an embodiment of the present invention;

[0027] Figure 4 Schematically shows a circuit diagram of a 4-stage PD traveling-wave electrode detector according to an embodiment of the present invention;

[0028] Figure 5 Schematically shows a parameter optimization flowchart according to an embodiment of the present invention;

[0029] Figure 6 Schematically shows the output frequency response curves of an 8-stage PD traveling-wave electrode detector array and a 4-stage PD traveling-wave electrode detector array according to an embodiment of the present invention.

[0030] [Description of the Reference Numerals]

[0031] 1 - grating; 2 - waveguide; 3 - power splitter; 4 - photodetector; 5 - traveling - wave electrode; 6 - termination resistor; 7 - output terminal. Specific embodiments

[0032] To make the objectives, technical solutions, and advantages of the present invention more clear and understandable, the following further elaborates on the present invention in detail with reference to specific embodiments and the accompanying drawings.

[0033] Figure 1 Schematically shows a flowchart of a method for improving the bandwidth of a traveling - wave electrode photodetector according to an embodiment of the present invention.

[0034] Please specifically refer to Figure 1 , the method for improving the bandwidth of a traveling - wave electrode photodetector in an embodiment of the present invention specifically includes operations S110 - S150.

[0035] In operation S110, an optical signal is coupled into the waveguide through a grating.

[0036] In operation S120, a multi - stage power splitter is used to divide the light in the waveguide into multiple optical signals with equal optical power, where the multiple optical signals with equal optical power are preset with a non - uniform designed optical path difference.

[0037] In operation S130, the multiple optical signals with equal optical power are input into corresponding multiple photodetectors.

[0038] In operation S140, when a photocurrent is generated in each photodetector, the photocurrent propagates in the traveling - wave electrode and generates reflection, where there is a phase difference between the multiple photocurrents.

[0039] In operation S150, the reflected photocurrent and the photocurrent propagating towards the output terminal are superimposed and output together.

[0040] Specifically, an optical signal is coupled into the waveguide through a grating, and a multi - stage 1 - to - 2 power splitter is used to divide the input light into multiple optical signals with equal optical power, and then input to the photodetectors. Among them, the optical path of each path of light is designed such that, compared with the traditional velocity - matching optical path, the optical path of each path is not arithmetic, but non - uniform, and the non - uniform designed optical path difference is converted into a phase difference of the photocurrent in the circuit.

[0041] When a traveling - wave electrode photodetector generates a photocurrent, the detector is equivalent to a current source. Due to the non - uniform optical path, there will also be a phase difference between the photocurrents. When the photocurrent propagates in the traveling - wave electrode, due to impedance mismatch, the current will be reflected, and the reflected photocurrent and the photocurrent propagating towards the output terminal are superimposed and output together.

[0042] It should be noted that the termination resistor is provided at the end side of the traveling-wave electrode. The termination resistor absorbs and reflects the photocurrent generated by the photodetector, and the size of the termination resistor can be 20 - 80 Ω.

[0043] Through the embodiments of the present invention, by designing the size of the termination resistor and the spacing between each photodetector, the influence of the phase difference on the bandwidth between the reflected photocurrent signal and the photocurrent signal propagating towards the output end is minimized. This impedance distribution optimization introduces optimization parameters such as the size of the termination resistor and the distribution spacing of the photodetectors, increasing the degree of design freedom, providing a greater optimization space for the traveling-wave electrode, and effectively improving the bandwidth of the traveling-wave electrode photodetector to meet the expected requirements.

[0044] Next, taking an 8-stage PD traveling-wave electrode detector and a 4-stage PD traveling-wave electrode detector as examples, the method for improving the bandwidth of the traveling-wave electrode photodetector will be described in detail.

[0045] Figure 2 Schematically shows the overall framework diagram of an 8-stage PD traveling-wave electrode 5 detector array according to an embodiment of the present invention; Figure 3 Schematically shows the overall framework diagram of a 4-stage PD traveling-wave electrode 5 detector array according to an embodiment of the present invention.

[0046] As Figure 2 shown, the 8-stage PD traveling-wave electrode 5 detector includes: a grating 1, a waveguide 2, a power splitter 3, a photodetector 4, a traveling-wave electrode 5, a termination resistor 6, and an output end 7, where; the grating 1, the power splitter 32, and the photodetector 4 are sequentially connected through the waveguide 2, the photodetector 4 is connected to the traveling-wave electrode 5, and both ends of the traveling-wave electrode 5 are respectively connected to the termination resistor 6 and the output end 7. Among them, the optical signal is coupled into the waveguide 2 through the grating 1; the power splitter 3 divides the light in the waveguide 2 into multiple optical signals with equal optical power, and the multiple optical signals are incident from both ends of the multiple photodetectors 4. Each photodetector 4 generates a photocurrent, the photocurrent propagates in the traveling-wave electrode 5 and generates reflection, and the reflected photocurrent and the photocurrent propagating towards the output end 7 are superimposed on each other and jointly output to the output end 7.

[0047] Please continue to refer to Figure 2 , the waveguide 2 is a single-mode silicon waveguide 2 with a thickness of 220 nm. The light entering the photodetector 4 will be divided into two beams by a 1×2 multimode interference type optical power splitter 3 (MMI), and the light incident on each photodetector 4 is in a double-end incident manner and enters the internal absorption region from both ends of the photodetector 4.

[0048] It should be noted that when designing the optical path of each path of light, compared with the traditional optical path with velocity matching, the optical path of each path is not arithmetic, but non-uniform. The non-uniform optical path difference is converted into the phase difference of the photocurrent in the circuit.

[0049] Please continue to refer to Figure 2 and Figure 3 , Figure 2 and Figure 3 The optical path differences Δl corresponding to the 8-stage PD traveling-wave electrode 5 detector array and the 4-stage PD traveling-wave electrode 5 detector array given are the additional optical delays compared to velocity matching. The optical path difference of the optical path needs to be converted into the phase difference of the electrical signal in order to perform optimization calculations in the circuit. Since the phase has periodic characteristics, the optical delay also has this characteristic. The corresponding relationship between the optical path difference and the phase difference of the photocurrent is as follows:

[0050]

[0051] where f is the frequency of the radio frequency signal generated by the photodetector 4, n is the effective refractive index of light propagating in the single-mode silicon waveguide 2, c is the speed of light in vacuum, Δl is the optical path difference, is the phase difference of the photocurrent.

[0052] This non-uniform design introduces multiple new design optimization parameters, and the number of optimization parameters is proportional to the number of photodetectors 4.

[0053] When the traveling-wave electrode 5 photodetector 4 generates a photocurrent, the detector is equivalent to a current source, and the photocurrent has a phase. Due to the non-uniform optical path, there will also be a phase difference between the photocurrents. When the photocurrent propagates in the traveling-wave electrode 5, due to impedance mismatch, the current will be reflected. The size of the termination resistor 6 and the spacing between each photodetector 4 are designed so that the reflected photocurrent signal and the photocurrent signal propagating towards the output end 7 have the least impact on the bandwidth due to the phase difference. This impedance distribution optimization introduces optimization parameters such as the size of the termination resistor 6 and the distribution spacing of the photodetectors 4, increasing the design freedom, having a larger optimization space for the traveling-wave electrode 5, and effectively improving the bandwidth of the traveling-wave electrode 5 photodetector 4 to meet the expected requirements.

[0054] It should be noted that the number of parameters of the spacing between adjacent photodetectors 4 is the same as the number of photodetectors 4, Figure 2 and Figure 3 gives the spacing ΔS between each detector of the 8-stage PD and the 4-stage PD, where ΔS8 refers to the spacing between the last detector and the termination resistor 6, and this spacing is usually small. For example, between each detector, in the direction from the input end of the traveling-wave electrode 5 to the output end 7, the spacing between every two photodetectors 4 increases in turn, and the spacing is 0 - 500 μm.

[0055] According to the above-mentioned design of the optical path difference, the spacing between adjacent photodetectors, and the parameters of the termination resistor, substitute them into the circuit to determine the parameters that meet the target bandwidth. Figure 4The circuit diagram of a 4-level PD traveling-wave electrode detector according to an embodiment of the present invention is schematically shown.

[0056] In an embodiment of the present invention, for the terminal resistance, its range is set to 20 - 80 Ω, because if the terminal resistance is too large or too small, it will cause the impedance mismatch to be too serious to obtain an ideal bandwidth; for the optical path delay parameter, since the phase of the photocurrent is periodic, the optical path delay is also periodic. Through the dependence calculation of the bandwidth and the optical delay, when the phase difference is π / 3, the magnitude of the optical delay is about 300 μm. Based on this optical path, the initial simulation can be carried out to determine that it has a significant impact on the bandwidth, and then determine that the magnitude of the optical delay is set in the range of 0 - 300 μm; for the spacing between each photodetector, according to the impedance current distribution principle, the spacing of the photodetectors closer to the terminal will be larger, and finally the parameter optimization range is set to 0 - 500 μm. After the parameter optimization settings are completed, the optimization objectives need to be set. The target bandwidth of PD-8 is set to 45 GHz, and the target bandwidth of PD-4 is set to 60 GHz.

[0057] As Figure 5 shown, Figure 5 The parameter optimization flow chart according to an embodiment of the present invention is schematically shown. After the above settings are completed, the calculation iteration starts. During the iteration process, the next parameter selection will be made according to the real-time calculation results, and finally the parameters corresponding to the bandwidth that meets the design requirements are obtained.

[0058] The optimization calculation results of the traveling-wave photodetectors PD-8 and PD-4 are given below.

[0059] The optimized parameters of each structure of the 8-level PD traveling-wave electrode detector array are shown in Table 1 below: where, R term = 35 Ω:

[0060] Table 1

[0061] Structure parameter (μm) <![CDATA[ΔS1]]> <![CDATA[ΔS2]]> <![CDATA[ΔS3]]> <![CDATA[ΔS4]]> <![CDATA[ΔS5]]> <![CDATA[ΔS6]]> <![CDATA[ΔS7]]> <![CDATA[ΔS8]]> Value 195 167 161 112 268 83 409 30 Structure parameter (μm) <![CDATA[Δl1]]> <![CDATA[Δl2]]> <![CDATA[Δl3]]> <![CDATA[Δl4]]> <![CDATA[Δl5]]> <![CDATA[Δl6]]> Δl7 <![CDATA[Δl8]]> Value 171 157 140 111 82 153 65 0

[0062] The optimized parameters of each structure of the 4-level PD traveling-wave electrode detector array are shown in Table 2 below: where, R term = 30 Ω):

[0063] Table 2

[0064] Structure parameter (μm) ΔS1 ΔS2 ΔS3 ΔS4 Value 196 138 251 30 Structure parameter (μm) Δl1 Δl2 Δl3 Δl4 Value 78 52 9 0

[0065] For the numerical values of the optical path difference optimization parameters, the photodetector closest to the termination resistor is used as the optical delay reference. Therefore, the optical path difference of the detector closest to the termination is always 0 (Δl8 and Δl4 in the table are 0). For the spacing parameters between adjacent detectors shown, the optimization results are similar to the expected results, with larger spacings for detectors closer to the termination resistor. Based on the above optimization parameter results, the bandwidth curves of the two devices are calculated, as Figure 6 shown, Figure 6 schematically showing the output frequency response curves of an 8-stage PD traveling-wave electrode detector array and a 4-stage PD traveling-wave electrode detector array according to an embodiment of the present invention. The bandwidth of the 8-stage PD reaches 49 GHz, and the bandwidth of the 4-stage PD exceeds 60 GHz.

[0066] In summary, the present invention provides a method for improving the bandwidth of a traveling-wave electrode photodetector. This method designs the optical path difference of the input optical path of the photodetector through photocurrent phase regulation. This optical path difference causes a phase difference in the photocurrents generated by each photodetector. When these photocurrents propagate in the traveling-wave electrode, they will be superimposed on each other. Optimizing the optical path difference maximizes the bandwidth of the final traveling-wave electrode photodetector. And by setting impedance distribution optimization, when the photocurrents generated by each photodetector propagate in the traveling-wave electrode, reflections will occur due to impedance mismatch. Designing the spacing between each detector to regulate the impedance distribution ensures that the reflected photocurrent and the photocurrent propagating towards the input end do not cause a decrease in the bandwidth of the traveling-wave electrode photodetector due to a phase difference.

[0067] Those skilled in the art will understand that although the present invention has been shown and described with reference to specific exemplary embodiments of the present invention, those skilled in the art should understand that various changes in form and detail can be made without departing from the spirit and scope of the present invention as defined by the appended claims and their equivalents. Therefore, the scope of the present invention should not be limited to the above embodiments, but should be determined not only by the appended claims but also by the equivalents of the appended claims.

[0068] Similarly, it should be understood that, in order to streamline the present invention and assist in understanding one or more of the various disclosed aspects, in the above description of the exemplary embodiments of the present invention, the various features of the present invention are sometimes grouped together into a single embodiment, figure, or description thereof. However, the disclosed method should not be construed as reflecting the intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as reflected by the preceding claims, the disclosed aspects lie in less than all the features of the single preceding disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into the detailed description, where each claim stands on its own as a separate embodiment of the present invention.

[0069] In the above specific embodiments, the objectives, technical solutions, and beneficial effects of the present invention have been further described in detail. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for improving the bandwidth of a traveling-wave electrode photodetector, characterized in that Including: The optical signal is coupled into the waveguide through a grating; A multi-stage power splitter is used to divide the light in the waveguide into multiple optical signals with equal optical power, wherein the multiple optical signals with equal optical power are preset with a non-uniformly designed optical path difference; The multiple optical signals with equal optical power are input into corresponding multiple photodetectors; When a photocurrent is generated in each of the photodetectors, the photocurrent propagates in the traveling-wave electrode and generates reflection, wherein there is a phase difference between the multiple photocurrents; The reflected photocurrent and the photocurrent propagating towards the output end are superposed with each other and output together.

2. The method for improving the bandwidth of a traveling-wave electrode photodetector according to claim 1, wherein The method further includes: A termination resistor is arranged at the end side of the traveling-wave electrode, and the termination resistor absorbs and reflects the photocurrent generated by the photodetector, wherein the size of the termination resistor is 20 - 80 Ω.

3. The method for improving the bandwidth of a traveling-wave electrode photodetector according to claim 1, wherein The corresponding relationship between the optical path difference and the phase difference of the photocurrent is: where f is the frequency of the radio frequency signal generated by the photodetector, n is the effective refractive index of light propagating in the single-mode silicon waveguide, c is the speed of light in vacuum, and Δl is the optical path difference, which is the phase difference of the photocurrent.

4. The method for improving the bandwidth of a traveling-wave electrode photodetector according to claim 1, characterized in that Each of the photodetectors uses double-ended incidence.

5. The method for improving the bandwidth of a traveling-wave electrode photodetector according to claim 3, wherein From the input end to the output end direction of the traveling-wave electrode, the distance between every two of the photodetectors increases in sequence, and the distance is 0 - 500 μm.

6. The method for improving the bandwidth of a traveling-wave electrode photodetector according to claim 1, wherein Each stage of the power splitter is a 1×2 multimode interference type optical power splitter.

7. The method for improving the bandwidth of a traveling-wave electrode photodetector according to claim 1, wherein The waveguide is a single-mode silicon waveguide with a thickness of 220 nm.

8. A traveling-wave electrode photodetector, characterized in that, Including: A grating, a waveguide, a power splitter, a photodetector, a traveling-wave electrode, a termination resistor and an output end, wherein; The grating, the power splitter and the photodetector are sequentially connected through the waveguide, the photodetector is connected to the traveling-wave electrode, and both ends of the traveling-wave electrode are respectively connected to the termination resistor and the output end.

9. The traveling-wave electrode photodetector according to claim 8, wherein The optical signal is coupled into the waveguide through the grating; The power splitter divides the light in the waveguide into multiple optical signals with equal optical power, and the multiple optical signals are incident from both ends of multiple photodetectors; Each of the photodetectors generates a photocurrent, the photocurrent propagates in the traveling-wave electrode and generates reflection, and the reflected photocurrent and the photocurrent propagating towards the output end are superposed with each other and output to the output end together.

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